The present invention relates to a substrate processing apparatus and a method for fabricating a semiconductor device; and, more particularly, to a substrate processing apparatus and a method suitable for reducing thermal stress in a wafer during a heat treatment process thereof.
Generally, a vertical hot-wall type batch heat treatment apparatus (referred to as a hot-wall type heat treatment apparatus hereinafter) is used for a heat treatment, such as an oxidization process and a diffusion process for fabricating an integrated circuit (IC).
The hot-wall type heat treatment apparatus includes a vertically arranged process tube and a heater positioned outside the process tube. The process tube has an inner tube and an outer tube that surrounds the inner tube, acting as a process chamber. After a plurality of wafers, each being horizontally arranged in a boat, are loaded into the inner tube via a furnace mouth positioned at a lower end portion of the inner tube, the heater applies heat to the process tube so that the wafers are heat-treated.
In the above-explained hot-wall type heat treatment apparatus, the boat usually includes a couple of end plates, three supporting members, and a plurality of supporting grooves. Each of the supporting members is vertically interposed between the couple of end plates, and the supporting grooves are inwardly opened at an equal interval along each of the supporting members. Three of the supporting grooves, each being included in a different supporting member but positioned on a same plane, provide a stage such that one of the wafers is located thereon. Consequently, the plurality of wafers are vertically arranged parallel to each other along the supporting members in the boat, wherein the centers of the wafers are aligned along a vertical straight line.
Since, however, each of the wafers is supported by three supporting grooves only, a rapid thermal stress may cause crystallographic defects (e.g., slip) in the wafer or, in certain cases, may entail a bending thereof. It is because the entire weight of the wafer is sustained only at a few points, so that concentration of tensile and load stress occurs at each contact portion between the wafer and the supporting grooves.
Japanese Patent Laid-Open Publication No. 1995-45691 discloses a wafer holder (referred to as a wafer supporting unit hereinafter) to avoid the above-mentioned problem, wherein the wafer supporting unit is made of a silicon carbide (SiC) in the shape of a circular ring on which a circumferential portion of the wafer is mounted. Since the entire weight of the wafer is sustained not by a few points but by an entire inner circumference of the wafer supporting unit, the wafer can be effectively prevented from slip formation, damage, or bending. In addition, the wafer supporting unit has an opening for a wafer suction plate (tweezers) to pass therethrough. Via the opening, the tweezers can load the wafer on the wafer supporting unit or unload the wafer therefrom while the wafer supporting unit remains supported by the supporting grooves in the boat.
Japanese Utility Patent Laid-Open Publication No. 1988-177035 discloses a wafer supporting unit for obtaining a uniform thickness of a chemical vapor deposition (CVD) film to be formed on the wafer. Such a wafer supporting unit includes a disk-shaped holder made of quartz (SiO2) and a horseshoe-shaped supporting member having a protrusion for preventing a movement of the wafer. The supporting member is mounted on the holder and the wafer is mounted on the supporting member. Since the supporting member has no stepped portion, a process gas can uniformly flow thereon, so that the CVD film formed thereon can achieve a uniform thickness.
Problems of the above-explained prior art are now discussed.
In the first prior art, because a wafer made of silicon directly contacts the wafer supporting unit made of silicon carbide, the wafer may abnormally stick to the wafer supporting unit, so that the resultant deformation of the wafer may entail the slip formation thereof. In the second prior art, because quartz is usually softened at a high temperature of above 1200xc2x0 C., the holder made of quartz may be deformed during the heat treatment process.
In another view, the wide opening of the first prior art wafer supporting unit as well as the second prior art horseshoe-shaped supporting member may result in a decreased temperature at a corresponding portion of the wafer. The partial difference in the temperature causes a poor uniformity of temperature distribution on the wafer, so that the CVD film formed thereon may have an irregular thickness.
It is, therefore, a primary object of the present invention to provide a substrate processing apparatus for reducing thermal stress of wafers during a heat treatment process.
In one aspect of the present invention, there is provided a substrate processing apparatus, which includes: a first holder made of silicon carbide or silicon; and a second holder made of quartz and mounted on the first holder, wherein the second holder is used to mount a substrate thereon while the substrate is being processed.
In another aspect of the present invention, there is provided a method for fabricating a semiconductor device using a substrate processing apparatus including a first holder made of silicon carbide or silicon and a second holder made of quartz, the method including the steps of: mounting a substrate on the second holder mounted on the first holder; and heating the substrate mounted on the second holder.